Reusable developing powder composition

Abstract

A non-fusible, monocomponent toner is described which comprises an organic resin having a high fusion point, a magnetically responsive material admixed therewith, and an electrically conductive surface. The toner is capable of being repeatedly used.

We claim: 
     
       1. A magnetically responsive developing powder of particles comprising an organic resin having a high fusion point and a glass transition temperature of at least 55° C., a magnetically responsive component admixed with said organic resin, and a layer of an electrically conductive, non-magnetizable powder secured to the surface of said particles, said electrically conductive powder having a particle size substantially smaller than that of said developing powder, wherein said developing powder is non-fusible at temperatures below 120° C. and has a maximum 23 hour secant number of 0.5 megohm. 
     
     
       2. A developing powder according to claim 1 further containing a fatty acid amide component containing at least about 10 carbon atoms secured to the surface of said particles. 
     
     
       3. A developing powder according to claim 2 wherein said electrically conductive material and said fatty acid amide are essentially permanently secured to said particles. 
     
     
       4. A developing powder according to claim 2 wherein said fatty acid amide comprises from 0.05 to 2% by weight of said developing powder. 
     
     
       5. A developing powder according to claim 2 wherein said fatty acid amide contains from 18 to 22 carbon atoms. 
     
     
       6. A developing powder according to claim 2 wherein said fatty acid amide is selected from the group consisting of erucamide, stearamide, behenamide, oleamide, N,N'ethylene-bis(tall oil)amide, and N,N'-ethylene-bis-oleamide. 
     
     
       7. A developing powder according to claim 6 wherein said fatty acid amide is erucamide. 
     
     
       8. A developing powder according to claim 2 further comprising a minor amount of a wax component having a melting point of at least 60° C. admixed with said organic resin and said magnetically responsive component. 
     
     
       9. A developing powder according to claim 8 wherein said wax component comprises up to 2.5 percent by weight of said developing powder. 
     
     
       10. A developing powder according to claim 1 comprising from 25 to 60 parts by weight of said organic resin, from 30 to 75 parts by weight of said magnetically responsive component, and from 5 to 10 micrograms/cm 2  of surface area of said developing powder of said electrically conductive, non-magnetizable powder. 
     
     
       11. A developing powder according to claim 1 having a maximum 23 hour secant number of less than 0.2 megohm. 
     
     
       12. A developing powder according to claim 1 wherein said electrically conductive, non-magnetizable powder is carbon black. 
     
     
       13. A developing powder according to claim 12 wherein said carbon black has a volatile content of less than 2 percent. 
     
     
       14. A developing powder according to claim 12 wherein said organic resin comprises a copolymer of styrene and n-butyl methacrylate. 
     
     
       15. A magnetically responsive, electrically conductive toner powder comprising particles containing (a) an admixture of a high fusion point organic resin having a glass transition temperature of at least 55° C. and a magnetically responsive component, and (b) a layer of a non-magnetizable electrically conductive powder having a particle size substantially smaller than that of said developing power, and a fatty acid amide component containing at least 10 carbon atoms, said layer being secured to the surface of said particles, wherein said toner powder is capable of being repeatedly used to develop an image formed on a receptor by an electrographic magnetic stylus electrode operating at 120° C. or less without fusing, wherein said toner powder has a maximum 23 hour secant number of 0.5 megohm.   
     
     
       16. A toner powder composition which comprises a plurality of particles capable of repeated reuse at temperature below about 120° C. without fusing, said toner having a maximum 23 hour secant number of 0.5 megohm, said toner comprising particles containing (i) a homogeneous blend of an organic resin which has a glass transition temperature of at least 55° C. and which does not fuse at temperatures below about 120° C., a magnetically responsive material, and a minor amount of a wax component having a melting point of at least 60° C., and (ii) a surface layer of a non-magnetizable, electrically conductive powder and a fatty acid amide component, said surface layer being securely attached to said particles. 
     
     
       17. A method of forming a developing powder comprising the steps of forming a dry blend of an organic resin having a high fusion point and a glass transition temperature of at least 55° C. and a magnetically responsive component,   heating said dry blend and mixing until a homogeneous mixture is obtained,   forming a solid mixture by cooling said molten mixture to less than the melting point thereof,   breaking the solid mixture into small particles,   dry blending the small particles at room temperature with a fatty acid amide containing at least 10 carbon atoms so as to loosely secure said fatty acid amide to the surface of said small particles,   blending the dry blended small particles with an electrically conductive, non-magnetizable powder at a temperature less than the melting temperature of said organic resin so as to embed said electrically conductive material on the surface of said particles, and   directing said blended particles at an angle of 90°±50° through a stream of gas heated to a temperature between about 370° C. and 425° C. for a time sufficient to essentially completely embed said electrically conductive, non-magnetizable powder and said fatty acid amide on the surface of said particles.   
     
     
       18. A non-fusing, monocomponent developing powder comprising an organic resin having a fusion point of at least 120° C., a magnetically responsive material admixed therewith wherein said powder has an electrically conductive surface layer therearound.